Add DefaultWebSocketClient to Rpc's project.json

src/Discord.Net.Rpc/project.json

@@ -13,6 +13,10 @@
     }
   },
 
+  "publishOptions": {
+    "includeFiles": [ "../Discord.Net.WebSocket/Net/DefaultWebSocketClient.cs" ]
+  },
+
   "configurations": {
     "Release": {
       "buildOptions": {